The present invention relates to methods of cleaning filter elements, particularly of the type including filter candles, by removing filter cake formed on the filter cloth of the filter element during filtration.
Conventional methods of releasing filter cakes from the surface of the filter cloth are usually performed after the filtering process has been completed.
During the filtration of liquids containing solid particles which should be separated from the liquid, filter cakes are usually built up on the filter cloth, which filter cakes are removed from the filter elements at the end of the filtration cycle.
Vibration of filtering elements with the filter cake formed thereon has been suggested for the removal of the filter cake. In such a method, vibrations are applied to the filter elements after the filtering process has been completed. The filter cake falls down on the bottom of the filter container and then is removed therefrom. This otherwise satisfactory cleaning process has the disadvantage that due to the application of vibrations to the filter element the filter cloth of the latter is so loaded that it may become defective.
One of the conventional methods of cleaning filter elements is disclosed in the German patent DE-PS No. 1,007,294. In the disclosed method pulsating movement is imparted to the filtering elements by pressure surges. For this purpose the filter candles are made elastic in the lengthwise direction thereof and during backwashing in this direction a pulsating movement under quickly changed pressures is imparted to a washing fluid flowing through the candles and thus to a filter cake formed on the filter candles, whereby the filter cake is separated from the filter cloth of the filter candles and drops. The filter elements or filter candles for this purpose are formed as folded bellows and for the additional elasticity wire coils are inserted into those bellows, which can expand in the lengthwise direction of the filter elements. As an additional stretching device a tension spring has been also suggested. All these movable mechanical components of the filter described in the German Pat. No. 1,007,294 are, however, subject to intensive wear. The conventional vibration movement imparted to the filter cloth has small amplitudes whereby total cleaning can not be accomplished in each case or this cleaning should take more time than desired.